Nanoparticle systems that can incorporate dopant entities have tremendous potential and are useful in a wide variety of contexts. There is a continuing need for improved systems. One particular goal in developing such systems is to provide imaging nanoparticles that can be utilized in surgery to define resection boundaries. Completeness of surgical resection profoundly impacts morbidity and mortality. The challenges and significance are particularly acute in surgery to remove tumors. In trying to achieve more complete tumor resections, the surgeon encounters several hurdles, which include irregular and indistinct tumor margins as well as tumor growth adjacent to or invading crucial physiological structures. A wide variety of techniques have been explored to date in an effort to better visualize tumor margins. However, there remains a continuing need for new and better probes and/or methods. In particular, there is an important, unmet need for a real-time probe/method for accurately detecting residual tumor.